294 ANATOMY OF THE GYMNOSPERMS 



Pits on the lateral walls of the ray cells 1-2, in the sum- 

 mer wood reduced to i, per tracheid. 



8. P. monticola. 

 Rays (tangential) nonresinous. 



Ray cells (tangential) oval, equal, and uniform. 



Pits on the lateral walls of the ray cells 1-2, or in 

 the marginal cells 3-4, per tracheid. 



9. P. flexilis. 



Ray cells (tangential), oblong, narrow, equal, and uniform. 

 Pits on the lateral walls of the ray cells 1-2 through- 

 out, rarely 3, per tracheid. 



11. * P. strobus. 



Ray cells (tangential) chiefly equal, but more or less vari- 

 able, from broadly to narrowly oval or oblong. 



Pits on the lateral walls of the ray cells 2 per tra- 

 cheid throughout, rarely I or 3. 



7. P. Lambertiana. 



Ray cells (tangential) oblong and narrow, more rarely 

 oval and broader, not very variable. 



Pits on the lateral walls of the ray cells i per tra- 

 cheid throughout, or in the early spring wood 2 

 per tracheid. 



12. P. parviflora. 



Resinous tracheids (radial or tangential) present, the resin in 

 plates opposite the rays and simulating Sanio's bands. 

 Rays (tangential) nonresinous. 



Ray cells (tangential) oval or oblong, not very variable. 

 Pits on the lateral walls of the ray cells i per tra- 

 cheid throughout, more rarely 2. 



13. P. albicaulis. 



Ray cells (tangential) oblong and narrow, more rarely 

 oval and broader, not very variable. 



Pits on the lateral walls of the ray cells i per 

 tracheid throughout, or in the early spring wood 

 2 per tracheid. 



12. P. parviflora. 



Sec. II. Pits on the tangential walls of the summer wood usu- 

 ally wanting. Medullary tracheids prominent, more or less, 

 often strongly, interspersed, their upper and lower walls den- 

 tate or the teeth so prolonged and united across the cavity as 

 to form a more or less dejinite and sometimes very strongly 

 defined reticulum. 



